In recent years, various electronic devices include a wireless communication function. Frequencies used for the wireless communication become higher when the data amount for communication become greater. For example, a high frequency band such as super high frequency (SHF) band or extra high frequency (EHF) band of which wavelength is shorter than that of ultra high frequency (UHF) band is now used. When the frequency becomes high, straightness of radio waves becomes excellent, and a gain of a certain direction becomes greater than gains of other directions, and thus, the radio waves have directivity. A single antenna has difficulty in controlling the directivity. Array antennas including a plurality of arrayed antenna elements can control direction and width of beam by controlling a phase of each antenna element, and can transmit and receive omnidirectional radio waves.
In an array antenna, a plurality of antenna elements and an electric circuit such as an amplifier may be accommodated in one chip. The electric circuit generates heat in operation. When the temperature of the array antenna increases, the quality of communication of signals to be transmitted/received decreases. Furthermore, latest models of electronic devices become thinner in consideration of mobility, and thus, the heat generated by the electric circuit of the array antenna easily transfers to the casing of the electronic device. This causes a surface temperature of the casing in the proximity of the array antenna increases and a user may be hurt by low temperature burns.